The present invention relates to a velocity controlling apparatus and method to be used with a stoker type burning apparatus on an incinerator for burning refuse such as domestic refuse, industrial refuse and the like (hereinafter called simply "refuse").
A known stoker type burning apparatus on a refuse incinerator comprises a drying stoker 3, a first combustion stoker 4 and a second combustion stoker 5 which are arranged to form stairs, as shown in FIG. 1. Each of the drying, first combustion and second combustion stokers 3, 4, and 5 is formed by a combination of movable fire grates and fixed fire grates, with the movable fire grates reciprocating back and forth at a predetermined velocity. A driving apparatus such as a hydraulic cylinder 8 activates a link mechanism 21 to give a reciprocating motion to movable fire grates 20, thereby imparting progressive movement to refuse deposited on the stokers to convey the same forward.
Consequently, the flow speed at which the refuse to be burned is conveyed by the reciprocating motion of the movable fire grates is nearly directly proportional to the speed of the reciprocating motion of the movable fire grates 20, i.e. the frequency of the reciprocating motion, that is, the number of cycles of the movable fire grates 20 measured in a unit length of time.
Refuse 2 fed into the refuse incinerator through a hopper 1 is placed successively on the drying stoker 3 and is dried thereon. The refuse thus dried is passed on to the first combustion stoker 4 for combustion and conveyed to the second combustion stoker 5 for complete combustion. Carbon left as residue is completely burned on the second combustion stoker 5, thereby turning the refuse into ash containing no combustibles, which is then taken out of the incinerator.
The refuse thrown into the incinerator varies day to day in kind of contents and in its humidity (hereinafter called "quality of the refuse"). Consequently, in order to completely burn the refuse as stated above, it is necessary to adjust the drying time, the combustion time and the time for burning carbon left unburned as residue, in accordance with the said quality of the refuse.
A known incinerator is adjusted by controlling the flow speed of the refuse conveyed on the stokers, that is, controlling how long the refuse remains on the drying, first combustion and second stokers 3, 4, and 5.
FIGS. 2 and 3 show an example of a method for regulating the speed of refuse flowing on the stokers in which the working speed of the hydraulic cylinder 8 is regulated by employing a variable-speed pump 6 as a hydraulic source or by controlling the amount of oil supplied with a flux control valve 7 on a fluid pipe. That is, frequency of the reciprocating motion of the movable fire grates as measured in a unit length of time is changed by controlling the working speed of the hydraulic cylinder 8, thereby regulating the length of time in which the refuse is on the stoker. Reference numbers 9, 10, and 11 (FIGS. 2 and 3) indicate a hydraulic pump, a leak valve and an electromagnetic valve, respectively.
But, the above stated methods in which the working speed of the hydraulic cylinder 8 is controlled by regulating the pumping capacity of the variable-speed pump 6 or by regulating the flux of fluid (quantity of fluid supplied) with a flux controlling valve 7 have the problem that fluid supplied to the hydraulic cylinder 8 continuously decreases because of increased leakage of fluid inside the hydraulic apparatus, referred to as "time wear", which occurs in connection with hydraulic control. The result is that a stabilized, constant, working speed of the hydraulic cylinder cannot be obtained.
Further, even if the quantity of fluid supplied to the hydraulic cylinder 8 is precise and stable, the problem with stabilization of speed of the reciprocating motion of the stokers remains unsolved since it is impossible to stop an increase of fluid leakage in the cylinder 8 caused by time abrasion of the cylinder piston of the cylinder 8 with the result that change of hydraulic load results in change of speed of the reciprocating motion of the stokers.